Vehicle restraint systems typically employ a reel with a flexible strap or other element wound thereon, a spring for urging the reel into strap retracted position and a mechanism for locking the reel automatically in emergency situations. One well known system utilizes a so-called inertia reel wherein an inertia mass senses acceleration on the strap to lock the reel at a predetermined level. Thus, if the strap is subjected to forces to extend the strap beyond a set acceleration, such as occurs when a person is suddenly thrown forward with respect to a vehicle, the strap acceleration will quickly lock the reel and prevent further extension of the strap. The term "acceleration" as used herein is intended to include "deceleration" as well.
In another known approach, an acceleration sensitive locking mechanism such as a pendulum is attached to the vehicle, and, if the vehicle is subjected to sudden stopping forces, the reel is locked to prevent further strap extension. While this approach is less direct with regard to the person wearing the strap, it has certain advantages over the strap acceleration device. For example, since the restraint harness straps must accelerate to lock the reel, the seat occupant must move out of the fully back, seated position for locking to occur, and there is thus some delay in locking. This may place the person in disadvantageous position for maximum crash protection or for taking some other action. With the use of a vehicle acceleration sensitive inertial locking system, added protection is supplied as the reel is locked during an initial crash pulse. Further, there are dangerous situations when locking is desired even though the strap is not withdrawn.
Since there are also some advantages to strap sensitive devices, it is desirable that a dual-mode system be provided, that is, strap sensitive and vehicle sensitive. There are, however, a number of additional aspects that should be considered for a satisfactory system. A vehicle sensitive mechanism should have the capability to lock a reel based on acceleration forces that can occur from a number of different directions. For example, in helicopter crashes, it is particularly important that a vehicle sensitive system function in situations in addition to crashes occurring while the vehicle is moving forward. Many prior vehicle sensitive systems have only one directional capability.
It is also highly desirable that any dual-mode system be integrated such that both the vehicle and the strap sensitive systems are provided within a single reel package. This is desirable for any application, but is particularly critical for military aircraft requirements wherein space and weight must receive premium consideration.
Some dual-mode systems are shown in earlier patents. U.S. Pat. No. 3,240,510 shows in FIGS. 26 and 27 a gimbal mounted pendulum carrying teeth forming a pawl or sear that cooperate with ratchet teeth of a reel to prevent rotation of the reel. Inertia forces acting on the pendulum weight in multiple directions are intended to produce reel locking action.
U.S. Pat. No. 4,515,326 to Karlsson discloses a horizontally oriented inertia disc which is driven by a member mounted on a vertical shaft which rotates through gearing in response to rotation of a reel. The interconnection between the inertia disc and the driving member is a plurality of balls positioned in mating recesses formed in the inertia disc and the driving member. Inertia forces acting on the inertia disc in any direction except toward the driving member will cause the inertia disc to move, against gravity, axially away from the driving member, and this axial movement is utilized to pivot a pawl so as to apply braking or locking action on the reel.
U.S. Pat. No. 4,109,881 discloses in FIGS. 26 and 27 a strap-sensitive inertia disc for triggering locking of a reel wherein an inertia ball positioned in a recess adjacent the periphery of the disc will wedge against the disc to produce locking action, when the ball is subjected to acceleration force as a result of forces applied to the vehicle.
Another known dual-mode system recently developed applies a pendulum for the vehicle sensitive inertia member together with a buckling spring column as a trip mechanism.
Another requirement for many military applications is that, once locked, the reel should remain locked until manually reset. Automatic unlocking could cause a "ratcheting out" effect in multiple pulse crash situations, therby allowing the torso to be in a disadvantageous position to withstand further shock pulses. Thus, a manual reset control must also be integrated into the system in a convenient, practical and reliable manner. Related to this, the inertia sensitive mechanisms used in combat aircraft must be designed so as to prevent inadvertent locking in flight. A pilot in combat does not need the distraction of having to recycle a manual control handle during a critical maneuver. The manual control should also permit manual locking as well as unlocking.
In spite of the foregoing known systems, a need exists for an improved dual-mode inertia reel restraint system that provides omni-directional vehicle acceleration sensitivity, as well as strap acceleration sensitivity in an integrated package, with a manual operational capability as well.